[FIXED] Get the second element in the array that fulfills some condition

Issue

Working on Android/Kotlin app, I'm having trouble finding indices of second and third element in the array that fulfills some condition. Since I know there are 4 elements in the array that would return true, i can use indexOfFirst() and indexOfLast(), but that way, I get only the first and the fourth indices.

val array: Array<String>

val firstOne = array.indexOfFirst(::func)
val lastOne = array.indexOfLast(::func)

fun func(element: String): Boolean{
   return element=="a" }

I tried using filterIndexed() but that returns a new list, and only values are saved, but not indices of the elements in there, which I need

Solution

You can use withIndex to get the items with their indices and then filter that.

val elements: List<IndexedValue<String>> = array.withIndex().filter { (_, value) -> func(value) }

If you only need indices:

val indices = array.withIndex().filter { (_, value) -> func(value) }.map { it.index }

Or if you want to assign each of these to a variable instead of getting a list:

val iterator = array.asSequence().withIndex()
    .filter { (_, value) -> func(value) }
    .iterator()

val (firstIndex, firstValue) = iterator.next()
val (secondIndex, secondValue) = iterator.next()
val (thirdIndex, thirdValue) = iterator.next()
val (fourthIndex, fourthValue) = iterator.next()

If you only need indices:

val iterator = array.asSequence().withIndex()
    .filter { (_, value) -> func(value) }
    .map { it.index }
    .iterator()

val first = iterator.next()
val second = iterator.next()
val third = iterator.next()
val fourth = iterator.next()

Answered By - Tenfour04
Answer Checked By - Clifford M. (JavaFixing Volunteer)